[JMPGuitars]

Are you measuring in the power supply or in the mic?

All measurements are in the mic. The rear diaphragm measurements are at the RD connection point referenced to ground.

Thanks,
Josh

[JMPGuitars]

I just tested pin 6 on the mic PCB, referenced to ground:

F8: 116V
C: 57V
O: 0V

That's obviously correct. Should I be seeing those same voltages on the RD? That doesn't make sense given the 250M series resistance between pin 6 and HZRD. I'm not sure why somebody said RD voltage is supposed to be that?

[Delta Sigma]

That's the last place you can check the voltage properly. 0, 2 and 4 volts seems right. If your DVM input impedance is 10M, in parallel with 250M puts you somewhere around 4.5V in fig-8.

[JMPGuitars]

That's the last place you can check the voltage properly. 0, 2 and 4 volts seems right. If your DVM input impedance is 10M, in parallel with 250M puts you somewhere around 4.5V in fig-8.

That's what I figured, so that's all good. Now I've got to figure out what's going on after that point. I installed the capsule and I'm getting very low output in all modes, but F8 is definitely louder than the others. Cardioid doesn't seem to work. Tapping the screen is louder than yelling at it. I'm guessing a connection issue somewhere.

[JMPGuitars]

Hahahahahaha. Well, I figured out the problem. I took some photos with my 42MP camera and zoomed in. Turns out, I didn't have to zoom in to see the problem. Can you see it?

[Delta Sigma]

Not sure. Backplate screw?

[JMPGuitars]

Not sure. Backplate screw?

lol, yup.

[JMPGuitars]

What's the general consensus regarding B+ with the M49b? I'm at 116V right now. What differences do people hear raising it to 118 or 120?

[Purplenoise]

What's the general consensus regarding B+ with the M49b? I'm at 116V right now. What differences do people hear raising it to 118 or 120?

For me it has to do with the capsule. In my 251 build I liked the b+ 118 when using the BeesNeez ck12 and 110 when using the Tim Campbell. As far as the 49 I use 115v cause that’s what is specified for the phaedrus ac701.

[JMPGuitars]

For me it has to do with the capsule. In my 251 build I liked the b+ 118 when using the BeesNeez ck12 and 110 when using the Tim Campbell. As far as the 49 I use 115v cause that’s what is specified for the phaedrus ac701.

I'm using a BeesNeez M7 capsule, with an AMI T47 transformer, and a 5840W NOS tube. I guess I should just experiment with it.

[Purplenoise]

I'm using a BeesNeez M7 capsule, with an AMI T47 transformer, and a 5840W NOS tube. I guess I should just experiment with it.

Yes that is the best way. I have found that in most designs when you go lower the sound gets kinda more compressed with an emphasis in mid frequencies..more reedy, and as you increase the b+ the sensitivity increases and the sound becomes more “electric” and detailed...more modern if you will. That’s not a scientific find but rather a personal observation on my builds.

[JMPGuitars]

Yes that is the best way. I have found that in most designs when you go lower the sound gets kinda more compressed with an emphasis in mid frequencies..more reedy, and as you increase the b+ the sensitivity increases and the sound becomes more “electric” and detailed...more modern if you will. That’s not a scientific find but rather a personal observation on my builds.

Thanks! That's exactly the kind of feedback I was looking for before experimenting.

[rmburrow]

I like cloning the Neumann NKM type supply for mic PS builds.  I especially like the way the HT is regulated by a VR tube (150B2 or US type 0A2) right off the rectifier through a resistor.  Additional RC pairs on the HT will drop the 150 vdc off the regulator and deliver clean stable voltage to the mic.  The heater voltage can be regulated using a LM317 or 7806 type circuit, or a series pass.  Instead of stabilytes in the NKM, rechargeable AA type batteries work.  Use enough of those in series for the heater voltage used.  Rechargeable batteries have lots of capacitance in a small volume.  Lots of possibilities; simple and inexpensive.

Note the 0A2 and 150B2 regulator tubes are not pin compatible.  Wire the socket accordingly.  Always use a small series resistor if batteries are used for final LV filtering.

[Purplenoise]

After plenty of experimentation and component swaps the mic is done. No more tweaking...sounding absolutely fantastic. The final version is:

-Danys D7 capsule ( wow...fantastic capsule)
-Moby bv11 7:1
-phaedrus ac701
-Cornell doubilier MP in wax 1uf 200v coupling cap
-wima tfm 0.01uf 400v caps
-Elna silmic 22uf cap

Calibrated at 115v b+ and 3.9v h+.

Very happy with this. Wonderful on both male and female voices and really nice on instruments.

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